Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory.
It acts to replace and recover from the activities of living. Its action is (almost always) the opposite of the sympathetic division. It activates the gut for digestion, slows the heart rate, decreases the blood pressure, etc. The autonomic nervous system controls the insides of the body: the viscera or gut.
In heart failure, the sympathetic nervous system increases its activity, leading to increased force of muscular contractions that in turn increases the stroke volume, as well as peripheral vasoconstriction to maintain blood pressure.he autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's fight-or-flight response. It is, however, constantly active at a basic level to maintain homeostasis.